1. Field of the Invention
The present invention generally relates to information processing devices and methods, and more particularly to an information processing device and method capable of displaying an image based on video data in different display formations such as a monitor display formation such as a RGB display formation and a television display formation such as an NTSC formation.
Recently, there has been a demand to display images formed by the RGB display formation on a television on which images are displayed in a predetermined television display formation such as the NTSC formation. The above demand has increased due to reduction in the cost of personal computers and development of various multimedia products. The personal computers use a RGB monitor on which images can be displayed in the RGB display formation. A television display formation such as the NTSC display formation, which is widely used, is capable of forming a large picture plane.
As is well known, the RGB display formation and the NTSC formation have different synchronizing signals and different numbers of scanning lines. Hence, if an image formed by the RGB video signal is displayed on an NTSC-formation display, it is necessary to convert the RGB video signal into a signal which conforms with the NTSC display formation.
2. Description of the Related Art
Generally, an information processing device has a plurality of picture-plane modes. Examples of such picture-plane modes are a 320.times.200 resolution mode, 640.times.400 resolution mode, and 640.times.480 resolution mode. These resolution modes use different synchronizing signals of, for example, 15 kHz, 24 kHz and 31 kHz. When one of the resolution modes is selected, the corresponding synchronizing signal is selected. A display unit detects the selected synchronizing signal with which video data is transferred, and alters the number of horizontal scanning lines. The RGB display formation can handle various display modes at the display unit side and is increasingly used.
Generally, a scan converter is used to convert video data in conformity with the RGB display formation into video data in conformity with the NTSC display formation. It will be noted that the RGB display formation can have an arbitrary number of horizontal scanning lines, while the NTSC display formation has only a predetermined single number of horizontal scanning lines. The scan converter is equipped with video memories designed to facilitate outputting image data in the NTSC display formation. More particularly, the video memory built into the scan converter has video memories which amount to one picture plane and each of such video memories has 200 horizontal lines. The video data output in the RGB display formation is subjected to a predetermined image process, and is written into other video memories in conformity with the NTSC display formation. When video data amounting to one picture plane is completely written into the video memories for the NTSC display formation, the video data stored therein is read in synchronism with the NTSC synchronizing signal.
As described above, the scan converter needs video memories suitable for the RGB display formation and other video memories suitable for the NTSC display formation. Hence, the conventional scan converter has a large circuit scale.
With the above in mind, an improvement has been proposed in Japanese Laid-Open Patent Application No. 6-118925, the disclosure of which is hereby incorporated by reference. This application discloses a device which converts video data formed in conformity with the RGB display formation into video data formed in conformity with a television display formation such as the NTSC formation.
More particularly, an instruction to output video data from a video RAM (VRAM) is given to the VRAM in accordance with a cycle defined by the ratio of horizontal scanning lines between the video data and a television signal. The video data thus read from the VRAM is cyclically latched in a plurality of buffers so that video data corresponding to one line is stored on one of the buffers. The video data cyclically latched in the buffers is subjected to an interpolation process in synchronism with the horizontal synchronizing signal of the television signal. In this way, the television signal having interpolated signal components is finally generated.
However, the device disclosed in the above application cannot function for outputting the RGB video data although the device can output the television signal obtained by performing the converting operation on the RGB video data.